from my experiences
Commercial/Editorial/Fashion - never had any big dramas so far, knock on wood
Weddings - IMO the worst clients are Viet wedding clients - because they see me as their 'kinsman' it does not give them the right to boss the hell out of me and my assistants, or take a few generations to decide to pay the remaining fee, or make ludicrous demands 'ie. photoshop my tattoo out in every single photo out of the 600 submitted', blah blah
my favourite and worst Viet client was a bridezilla in Melb - day after the wedding she came over with her groomsman and groom demanding all her photos right now, with a portable hard drive in hand. I said they are RAWs only and wont be ready for a few weeks. But they got angry and abusive, and I didnt want any troubles and just gave it to them - and then she goes home and complains she cannot open them hahahahahaha! Makes you wonder what sort of person she is as there were many tables at her wedding empty due to her own friends and grooms friends deciding not to turn up
when you shoot enough weddings you will see a plethora of nonsense and ridiculous things, and see the good and bad sides of people very quickly.